Different methods for preserving two or more reagents, in order to put them in contact only when they have to be used for a rapid antigen extraction, are known in the state of the art. For example, in pharmaceutical preparations, a reagent is commonly preserved in a solid state and it is dissolved in a liquid state solvent just before the use, by perforating a mechanical partition wall.
Other preservation methods have been described as well, in which two or more containers, each containing a reagent, are inserted into a single main container inside which, after the breakage of the internal containers, the reagent mixing takes place.
The traditional methods of extraction of saccharidic antigens of group A streptococcus provide for the use of liquid reagents (Lenneft, E. H., Ed., Manual of Clinical Microbiology, Fourth Edition, American Society of Microbiology, Washington, D.C., 1985, pages 170-171). Typically, two liquid reagents are used in the extraction stage: an acid (acetic, hydrochloric or citric acid) and a sodium nitrite solution. The two reagents are mixed in a test tube in which the wad used to take the biological sample to be examined is inserted.
In other known methods, at least one of the two reagents is in a solid state (U.S. Pat. No. 5,536,646), or the reagents are contained in test tubes or flasks with several separate compartments, each containing a single reagents to be mixed immediately before use (U.S. Pat. No. 4,673,639).
By mixing the two reagents, nitrous acid, which is a relatively unstable acid, is produced, thus requiring that the reagents are mixed immediately before the extraction process starts. Otherwise, the instability of the resulting nitrous acid solution can reduce the extraction effectiveness. In fact, if the reagents are prematurely mixed with respect to the biological sample addition, according to what described in U.S. Pat. No. 4,851,337, the nitrous acid decomposition takes place and the extraction solution can lose its effectiveness in a very short time.
According to the method described in U.S. Pat. No. 5,415,994, the extraction takes place in a well directly obtained in the cartridge containing the immunochromatographic strip. One of the two reagents is contained in a flask, that contains on its turn a phial with the second reagent. The operator mixes the two reagents by breaking the phial and then pours the mixture in the well in which the wad is placed. In this way, the operator does not have to count the drop number of each reagent. However, in this case too the extraction takes place after the two reagents have been mixed. Moreover, the insertion of the wad in the well sometimes causes the even partial occlusion of the liquid drainage conduit and thus the flow is slowed down or even blocked. Otherwise, if the wad is inserted in a manner such that the liquid does not flow therethrough before reaching the immunochromatographic chamber, the reaction liquid can reach the immunochromatographic membrane before the extraction takes place.
According to other known methods (U.S. Pat. No. 5,494,801), a third reagent is added to the two default ones in order to neutralize the solution before the chromatographic stage takes place. At present however the use of three reagents is considered too complicated for the operator, and thus the systems providing for the use of two reagents only are preferred. Furthermore, even these methods do not avoid the risk of effectiveness reduction of the extraction due to the time elapsed between the reagent mixing and the sample insertion.
Methods that provide for the insertion of the sample, on which the extraction has to be performed, in a device before adding the reagents have been described too (U.S. Pat. No. 6,168,956). In these methods, the operator must apply the reagents according to the optimal time sequence. However, the need to determine the volume of the reagents (for example, by counting the reagent drops) still remains, as well as the possibility to use the same reagents twice.
The traditional methods of extraction of lipopolysaccharidic antigens from Chlamydia trachomatis provide for the use of an alkaline reagent able to extract the lipopolysaccharidic antigens, in which an acid or a buffer is inserted to neutralise the extraction. According to a traditional method, the alkaline reagent consists of sodium hydroxide and the aid reagent for neutralizing the extraction solution is hydrochloric acid.
The wad through which the biological sample has been taken is inserted into a test tube containing the alkaline reagent for the extraction and it is agitated for a predetermined time, after which the neutralization reagent is added.